A tropical disturbance southeast of Guam is expected to develop into a tropical depression by late Thursday afternoon as it passes west of Rota, according to the National Weather Service.
Forecasters said that after the system passes the area, a monsoon surge is expected to prolong showers, thunderstorms, and gusty winds across the Marianas into the weekend.
At 7 p.m. Wednesday the system was centered near 12.9 degrees north latitude and 145 degrees east longitude.
Rainfall of 6 to 12 inches is possible across the region through Saturday night, and a flash flood watch is in effect for Guam, Rota, Tinian and Saipan through late Saturday night.
A high surf advisory is in effect for Guam, Rota, Tinian, and Saipan from 6 p.m. Thursday to 6 a.m. Sunday along south and east facing reefs. Large breaking waves of 8 to 11 feet are expected in the surf zone. Dangerous swimming and surfing conditions and localized beach erosion are expected.
A high risk of rip currents is in effect for Guam, Rota, Tinian, and Saipan from Thursday morning through late Thursday night along east facing reefs and from Thursday evening through late Saturday night along south and west facing reefs.
Forecasters have said the rip currents will be life-threatening.
A small craft advisory is in effect for the coastal waters of Guam and Rota from 6 a.m. Thursday to 6 a.m. Sunday. South to southwest winds of 15 to 25 knots, with gusts to 40 knots, and seas of 8 to 12 feet are expected.